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Origin of paleosubduction-modified mantle for Late Cretaceous (~100 Ma) diabase in northern Guangdong, South China: Geochronological and geochemical evidence
Lithos ( IF 3.5 ) Pub Date : 2020-10-01 , DOI: 10.1016/j.lithos.2020.105603
Hai Jiang , Shao-Yong Jiang , Kui-Dong Zhao , Wen-Qian Li , Hui-Chuan Liu

Abstract Cretaceous mafic rocks mainly occur along the coast of South China. In comparison, coeval mafic rocks are distributed only sporadically in the inland region, and their petrogenesis and tectonic setting have not been well documented so far. Here we report a detailed study on 40Ar/39Ar dating, elemental geochemistry and Sr-Nd-Pb isotopes for the Yaoling diabases in northern Guangdong, South China. The Yaoling diabases yield a Late Cretaceous (101 ± 1 Ma) 40Ar/39Ar age. These rocks have variable (87Sr/86Sr)i (0.705023–0.709847), relatively uniform eNd(t) (+2.45 to +3.88) and intermediate (206Pb/204Pb)i (18.586–18.692), (207Pb/204Pb)i (15.743–15.764) and (208Pb/204Pb)i (38.300–39.137). These rocks exhibit geochemical affinity to both within-plate and arc magmatism, i.e., relatively high TiO2, Nb and Zr contents, and negative Nb anomalies with (Nb/La)PM of 0.65–0.82. Such dual features indicate that the Yaoling diabases were most likely generated through partial melting of a previously metasomatized lithospheric mantle at a shallow depth (75–85 km), and modified by crystal fractionation. It is likely that the ancient metasomatism may have occurred during the Neoproterozoic oceanic subduction beneath the Cathaysia Block. We suggest that the Yaoling diabases formed in an intraplate extension setting associated with asthenospheric upwelling, possibly in response to the far-field stress that propagated from the paleo-Pacific subduction during the Late Cretaceous (ca. 100 Ma).

中文翻译:

华南粤北晚白垩世(~100 Ma)辉绿岩古俯冲改造地幔成因: 年代学和地球化学证据

摘要 白垩纪基性岩主要产于华南沿海。相比之下,同时代的镁铁质岩在内陆地区仅零星分布,其岩石成因和构造环境迄今尚未得到很好的记录。在这里,我们报告了对华南广东北部耀岭辉绿岩的 40Ar/39Ar 定年、元素地球化学和 Sr-Nd-Pb 同位素的详细研究。耀岭辉绿岩产生晚白垩世 (101 ± 1 Ma) 40Ar/39Ar 年龄。这些岩石具有可变的 (87Sr/86Sr)i (0.705023–0.709847)、相对均匀的 eNd(t)(+2.45 至 +3.88)和中间 (206Pb/204Pb)i (18.586–18.692)、(204Pb) (204Pb)/2 15.743–15.764) 和 (208Pb/204Pb)i (38.300–39.137)。这些岩石对板内和弧内岩浆活动都表现出地球化学亲和力,即相对较高的 TiO2、Nb 和 Zr 含量,和负 Nb 异常,(Nb/La)PM 为 0.65–0.82。这种双重特征表明,耀岭辉绿岩最有可能是由先前交代化过的浅层岩石圈地幔(75-85 公里)部分熔融产生的,并通过晶体分馏进行了修饰。古老的交代作用很可能发生在华夏地块下方的新元古代大洋俯冲过程中。我们认为耀岭辉绿岩形成于与软流圈上升流相关的板内伸展环境中,可能是对晚白垩世(约 100 Ma)古太平洋俯冲传播的远场应力的响应。这种双重特征表明,耀岭辉绿岩最有可能是由先前交代化过的浅层岩石圈地幔(75-85 公里)部分熔融产生的,并通过晶体分馏进行了修饰。古老的交代作用很可能发生在华夏地块下方的新元古代大洋俯冲过程中。我们认为耀岭辉绿岩形成于与软流圈上升流相关的板内伸展环境中,可能是对晚白垩世(约 100 Ma)古太平洋俯冲传播的远场应力的响应。这种双重特征表明,耀岭辉绿岩最有可能是由先前交代化过的浅层岩石圈地幔(75-85 公里)部分熔融产生的,并通过晶体分馏进行了修饰。古老的交代作用很可能发生在华夏地块下方的新元古代大洋俯冲过程中。我们认为耀岭辉绿岩形成于与软流圈上升流相关的板内伸展环境中,可能是对晚白垩世(约 100 Ma)古太平洋俯冲传播的远场应力的响应。
更新日期:2020-10-01
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